This invention relates generally to subsurface well apparatus for propagating explosive shock waves for detonation of explosive charges within a wellbore penetrating subterranean formations.
It has become common practice in the completion of oil and gas wells to perforate the well casing and the surrounding formations to bring a well into production. One typical perforating device comprises detonating explosives of high energy and of the general character and form known as "shaped charges". In a typcial embodiment, a plurality of shaped charges are mounted in a fluid-tight, cylindrical housing or on an elongated bar member which is adapted to traverse a well to be perforated. The shaped charges may be mounted in a variety of patterns along a length of the carrier member, with the axis of perforation directed generally laterally therefrom. A plurality of carrier members may be mechanically serially linked together to provide for perforating the casing and surrounding formations over a desired vertical interval.
When performing a perforating operation over a vertical length of a well, a plurality of perforating gun assemblies may be mechanically and explosively coupled in end-to-end fashion to provide detonation and thus perforating capability over the desired gun length. One method common in the prior art for explosively linking together a plurality of perforating guns is by splicing together lengths of detonator cord. This method may include the use of a side-by-side or butt contact splices of a detonating cord proximate the mechanical gun joints. These methods typically require that the detonator cord be spliced together through a port provided in the side of the gun body or mechanical coupler member. Another method common in the prior art includes using sensitive, primary explosives installed on the detonator cord proximate the mechanical gun joints. These primary explosives serve to propagate the detonating wave from one gun member to the next. The detonator cord splicing method makes gun assembly more difficult thereby substantially increasing the time required, while the use of exposed primary initiating explosives proximate the mechanical gun joints presents a substantial safety hazard from premature detonations during gun assembly.
Yet another method includes the use of an explosive wave propagation assembly having no primary explosives and typically employing a shaped charge to propagate a detonating wave from gun assembly-to-gun assembly. This propagation assembly is connected to the detonator cord inserted into the end of each gun assembly prior to assembly as a complete unit. This typically results in excessive "slack" in the detonator cord within a gun assembly which can result in improper propagation of the detonating wave causing a misfire of the shaped charge perforating devices mounted therein.
These and other disadvantages are overcome with the present invention by providing a method and apparatus for perforating well casing and the surrounding formations using an explosive wave propagation system having no primary explosives and requiring no splicing of a detonator cord and allowing removal of excessive slack from the detonator cord.